Egypt's defense minister said today that an "isolated" group of four men led by a Moslem extremist soldier carried out yesterday's bloody assassination of President Anwar Sadat at a suburban Cairo parade ground.

As the government moved swiftly to carry out an orderly transfer of power, Defense Minister Abdel Hamlim Abu Ghazala, wearing bandages on his right arm and left ear from the attack, told the National Assembly that the men who cut down Sadat with automatic weapons fire had acted on their own, without outside help.

"There was no coup," he told the National Assembly in a trembling voice. "It is an individual group and they are not even related to any other group or country."

Abu Ghazala said only four persons were involved in the shooting, but many eyewitnesses reported seeing at least eight, not including the driver of the truck carrying the men. The attackers, dressed as soldiers, were part of a military parade being viewd by Sadat and other dignitaries.

"One of the soldiers was a Moslem fanatic, and he did it. That's all," said Abu Ghazala.

Western diplomatic sources lent credence to reports circulating widely in the capital that the assailants were Moslem extremists belonging to the secret organization known as Takfir wa Hijra (Repentant and Holy Flight), which was involved in earlier terrorist activities against the Sadat regime.

"They the authorities are increasingly convinced, not just from guessing but interrogation that this is the group," one source said.

In addition to having a strong presence among Egyptian youth and on campuses here, Takfir wa Hijra is known to have some following within the Egyptian military, although the exact extent of its support has never been clear. Today, unofficial Egyptian sources and Western diplomats echoed the assertion of U.S. Secretary of State Alexander M. Haig Jr. that the group was "centered, not exclusively, in certain military units."

Ghazala, however, sought to downplay in his remarks to the assembly any implication that high-level elements within the Army were involved in the assassination. And though the assailants were clearly influential enough to gain access to the parade and ammunition for their weapons, the absence of additional movements toward a coup indicated that they did not have the power to direct the bulk of the Army.

Reuter quoted Abu Ghazala as telling Egyptian reporters 2nd Lt. Khaled Attallah led the assassins, having given his assigned men a vacation and recruited in their place two civilians with past military service plus another officer on inactive reserve.

While investigations of the assassins continued, National Assembly Speaker Sufi Abu Taleb was formally sworn in as interim president of the republic and the assembly overwhelmingly voted to endorse the ruling party's nomination of Vice President Hosni Mubarak as Sadat's permanent successor. An official statement said a national referendum would be held next Tuesday to approve the decision.

Thus, if all goes according to schedule, Mubarak, 52, will take over by the middle of next week as the third president of Egypt's republic since the overthrow of the monarchy here in 1952.

At the same time, the government set the state funeral for the slain president at noon Saturday amid announcements that among those attending the ceremony will be Israeli Prime Minister Menachem Begin, former U.S. presidents Jimmy Carter, Gerald R. Ford and Richard M. Nixon and a delegation of the Reagan administration headed by Haig.

The plans of three former U.S. presidents to attend the funeral underlined Sadat's importance in the balance of power in the Middle East and the global implications of the quick barrage of grenades and gunfire that killed him.

Both Egyptian officials and Western diplomatic sources said the government's main objective in the present crisis was to carry out a calm transfer of authority and maintain the appearance of order, stability and continuity of policy in the face of widespread concern abroad about the nation's future direction.

Those same diplomatic sources said there was no evidence so far that the assassination team, which launched its attack from a military truck passing in front of the reviewing stand where Sadat and much of the rest of the Egyptian power elite was seated, intended to wipe out the entire leadership or overthrow the political system built by Sadat over the past 11 years.

However, many officials around Sadat were struck by the fire, and reports about the number of killed and injured continued to vary throughout the day. By late tonight, the government had still not provided an official list.

The number of those believed to be dead dropped from nine to eight or seven with the news that Fawzi Abdel Hafez, Sadat's private secretary, had not died as first reported and that the North Korean ambassador, one of a number of foreigners hit in the spray of bullets from the assailants' guns, was still alive.

The death toll may still rise, however, as a number of the roughly 30 wounded persons are still in critical condition.

Initial reports yesterday had indicated that another Islamic fundamentalist group, the Moslem Brotherhood, was probably connected to the assassination. Both the Brotherhood and Takfir wa Hijra were prime targets of Sadat's massive crackdown on religious extremists and opposition elements last month, in which more than 1,500 persons were arrested.

Egyptian and Western diplomatic sources ruled out the likelihood today that a third group, based abroad and led by dissident retired Army chief of staff Saadeddin Shazli, was responsible for the shooting. Yesterday, anonymous Arabs calling Western news agencies in Beirut claimed the assassination had been carried out by Shazli's group, which is backed by Libya and Syria and has been referred to by several names, including the Egyptian National Front and the Organization for the Liberation of Egypt.

Local press reports said security authorities have captured three or four of the assailants and had killed one or two others.

One report said three of the six were military officers and that one of them, a major, had had a brother arrested in the crackdown on Moslem extremists last month.

Western diplomats and analysts continued to puzzle today over the absence so far of any major public demonstration of grief over Sadat's assassination, in contrast to the dramatic displays that greeted the death of his precedessor, Gamal Abdel Nasser, in September 1970.

The day began at 5 a.m. with chantings from the Koran blaring through loudspeakers at the city's mosques, and incense sellers wandered from cafe to cafe, trailing thick fumes.

But the incense was meant to purify the air for an upcoming religious holiday, not commemorate Sadat's funeral, and Egyptians interviewed in the street, while expressing shock and dismay at what had happened, seemed too confused or uncertain to react more demonstratively.

Dassim Khatib, owner of a pharmacy in downtown Cairo, called the "accident" absolutely terrible. "The streets are calm," he said, "but everyone is listening and talking about what is going to happen next."

Everywhere today in this sprawling Nile Valley city of 12 million, people could be seen huddled around in small groups, looking at the often spectacular pictures of the assassination in the local press. Faces were somber and sometimes tense, but few tears were being shed.

In fact, only in the National Assembly, where deputies gave emotional eulogies to the slain president, was there any real sign of emotion over Sadat's death. Many deputies had tears in their eyes.

Elsewhere, business was very much as usual. The markets and butcher shops were filled with customers busy preparing for the four-day Moslem holiday of Id Al Adha. Banks were open, and there was no change in exchange rates, official or black-market, despite the jittery reaction on world currency markets.

At the fashionable Gezirah, a playground of the Egyptian middle class where Sadat had much support, there was an enormous crowd of people going about their business as usual.

Western diplomats were at a loss to explain the relative lack of reaction, but some ascribed it to general numbness, the upcoming holiday or simply uncertainty about what was going to happen next.

"Sadat was clearly out in front in a lot of things he was doing," said one diplomat, referring to Egypt's peace treaty with Israel and economic liberalization measures. "People were waiting for proof of the pudding that was not there yet."

There was much speculation here today about the future course of the regime under Mubarak, who to date has carefully avoided a high profile, playing the role of understudy with the same discretion that Sadat displayed under Nasser.

A former commander in chief of the Air Force and vice president since 1975, Mubarak is thought to have a strong standing in both the military and the government, where he often led Cabinet meetings and missions abroad for Sadat.

One diplomat described him as "energetic" and "confident of his judgment," and doubted there would be another power struggle after his takeover next week like the one Sadat faced in the first years of his rule.

Sadat, this diplomat said, had been widely held at first to be only an interim leader, while Mubarak did not face such a perception.

Furthermore, all of those at the top level of the Sadat government, foremost among them Mubarak himself, had a "strong commitment to finishing the job Sadat started" both in foreign and domestic policy, the diplomat remarked.

The new Egyptian leader is expected to be even tougher than his predecessor with the legal opposition, take a very strong stand against the activities of the Moslem fundamentalists and generally set a more authoritarian style of rule.

Nonetheless the diplomat, a longtime observer of both Sadat and Mubarak, predicted the latter would initially accept "a more collegial kind of leadership," at least until he is better established.